The invention is useful for sealing the passage of a drive shaft from a motor compartment to a hydraulic unit in submersible pumps and mixers, e.g., albeit other use is conceivable. The submersible pumps and mixers typically comprise an electrically driven motor and a hydraulic unit comprising an impeller/propeller connected to the motor via a rotary shaft. In order to prevent medium in the hydraulic unit from entering the motor along the shaft, seal devices are arranged between the hydraulic unit and the motor. A common type of seal device is a mechanical seal comprising a seal ring rotating with the shaft and sealing against a stationary seal ring which is attached to a housing wall forming part of the motor compartment. The two seal rings are pressed towards each other by spring force to prevent medium from entering the sealing interface.
In submersible pumps, e.g., a set of two seal assemblies are often installed to provide sealing interfaces at the passages of a drive shaft reaching through a fluid filled housing portion which defines a barrier for pumped medium, between the motor and the hydraulic unit.
The seal assemblies which are referred to generally comprise a ring-shaped, axial face seal member presenting a sealing end face, which is biased towards the stationary seal ring on the housing wall by means of a spring. The spring is supported from a supporting member that is non-rotatably connectable to the drive shaft, and at an axially fixed position which sets the seal member under bias from the spring. The seal and supporting members are likewise non-rotatably connected, and so the seal assembly is supported on the drive shaft for co-rotation therewith, and in concentric relation with the drive shaft.
Since the sealing faces are subject to wear, ease of mounting and dismounting is an important feature in an axial face seal assembly. In many rotary machines the space available about the drive shaft is however limited, and replacement of the seal assembly requires in most designs that the machine housing is opened. For ease of mounting and replacement there is thus a need for a seal assembly which can be axially and non-rotatably secured to the drive shaft in mounting and dismounting procedures requiring axial access only to the seal assembly.
To this purpose, Lutes has disclosed in U.S. Pat. No. 6,364,605 a turbine pump wherein a carrier member for an axial face seal is non-rotatably secured to the drive shaft by means of a drive pin. The drive pin reaches in radial direction from the carrier member into an axially extended key-groove running in the surface of the drive shaft, the key groove also cooperating with a key for securing an impeller in the drive shaft's end. A snap-ring which is insertable in a snap-ring groove on the drive shaft secures the carrier member axially on the drive shaft. As the seal assembly is inserted on the drive shaft, the drive pin travels in the key-groove which mouths in the end of the drive shaft. The snap-ring is then pushed axially over the drive shaft to be seated in the snap-ring groove, under compression of the seal assembly.
Although Lutes' solution meets the stated object well, the structure requires dedicated and accurate machining of the drive shaft in order to fit a specific seal assembly.
In U.S. Pat. No. 5,558,343 Aparicio discloses an axial face seal assembly in a water pump wherein an impeller is connectable to the end of a drive shaft. The seal assembly comprises, in consecutive order, a wear disc presenting a sealing end face, an annular seal member supported in a carrier which is arranged to slide on the drive shaft, a compression spring urging the carrier, the seal member and the wear disc away from a base member which is axially and non-rotatably securable to the impeller, and thus relative to the drive shaft. In its bottom end facing away from the carrier, the base member is formed with a radial flange which is supported axially from the back of the impeller. A stop pin rises from the impeller's back to engage a tab in an annular channel formed in the flange of the base member, the stop pin securing the base member non-rotatably to the impeller. The base member and the carrier are non-rotatably engaged by means of interlocking radial protrusions and openings which are formed in the cylinder walls of the two elements, and which permit an axial relative motion between the two.
Albeit Aparicio's solution meets the object of a mounting procedure requiring axial access only, the structure inconveniently falls out of the housing if the impeller was to be dismounted for replacement. In U.S. Pat. No. 5,558,343 this is no problem, since the seal assembly is intended to remain mounted for the service life of the pump itself.